1. Related Application
The present application claims priority to Japanese Patent Application Number 2007-292223, filed Nov. 9, 2007, the entirety of which is hereby incorporated by reference.
2. Field of the Invention
The present invention relates to methods and apparatuses for generating bird's-eye view images. More specifically, the present invention relates to a method and an apparatus for generating a bird's-eye view image, as viewed from a virtual viewpoint above a vehicle, by performing viewpoint conversion processing on an image of the surroundings of a vehicle photographed by a camera.
3. Description of the Related Art
Conventional technology exists that captures images of surroundings of a vehicle by using multiple cameras installed at the front, rear, left, and right portions of the vehicle. Viewpoint conversion processing may be performed on the captured images in order to generate a bird's-eye image as viewed from a virtual viewpoint above the vehicle (this bird's eye image will hereinafter be referred to as a “vehicle-surroundings bird's-eye image”). The generated bird's-eye view image of the vehicle's surroundings may then be displayed on a display device, for example, as disclosed in Japanese Patent No. 3300334.
In addition, it is known in the art to perform viewpoint conversion processing on an image of the area surrounding a vehicle photographed by a camera installed at a predetermined position on a vehicle to generate a bird's-eye view image viewed from a virtual viewpoint thereabove (this bird's-eye view image will hereinafter be referred to as a “one-directional bird's-eye view image”) and display the one-directional bird's-eye view image on a display device.
According to the vehicle-surroundings bird's-eye view image display technology and the one-directional bird's-eye view image display technology (which are hereinafter collectively referred to as “bird's-eye view image display technology”), a driver can prevent a collision and so on of the vehicle with obstacles located in the area surrounding the vehicle by recognizing the positional relationships between the vehicle and the obstacles shown in the vehicle-surroundings bird's-eye view image or the one-directional bird's-eye view image displayed on a display device in the vehicle.
In conventional bird's-eye view image display technology, the viewpoint conversion processing performed on the image or images captured by the camera by setting a projection plane at the height of a road surface in the vehicle's surroundings. Pixels of the captured image(s) are then projected onto the projection plane. Since the height of the road surface is used as a reference for the viewpoint conversion processing, a three-dimensional obstacle is displayed with a shape that falls away from the vehicle, as viewed from the camera, relative to a portion at which the obstacle makes contact with the ground. Since the absolute distance on the road surface between the vehicle and the obstacle is accurately expressed for three-dimensional obstacles disposed on the surface of the road, the bird's-eye view image gives the driver a somewhat correct sense of distance between the vehicle and the obstacle(s) in its surroundings.
However, when the obstacle in the vehicle surroundings is a three-dimensional object having a portion (hereinafter referred to as a “predicted contact portion”) projecting toward the vehicle and disposed at a certain height above the road surface such that the predetermined contact portion may make contact with the vehicle before the portion of the object contacting the surface of the road when the vehicle moves toward the object, using conventional technology, the projection of an image of the predicted contact portion in a bird's-eye view results in the predicted contact portion being displayed at a distance that is farther from the vehicle than the actual distance between the vehicle and the predicted contact portion. Thus, problems exist in that when the vehicle moves toward the obstacle, the driver may have a sense of discomfort due to, for example, a sudden approach of the obstacle, or alternatively, the driver may not be able to perform a stopping operation in time to avoid colliding with the obstacle/object.
One example of an obstacle that may cause such problems is a clothes-drying pole. That is, when two stands disposed at opposite ends are not located in the direction the vehicle is moving, and a pole placed across the stands is located in the direction the vehicle is moving, the pole acts as the predicted contact portion of the obstacle that causes the above-described problems. Other examples of obstacles that cause the above-described problems include a three-dimensional object that has a shape extending substantially upward from the road surface and that bends or curves toward the vehicle. Another example includes an object having a shape that has a portion protruding toward the vehicle at a predetermined height on a wall located in the direction of movement of the vehicle. Obstacles causing such problems will hereinafter be referred to as “aerial obstacle(s)”.
FIGS. 13A and 13B are schematic views illustrating the above-described problems of the related art. FIGS. 13A and 13B show the principle of how the predicted contact portion of an aerial obstacle is displayed at a position that is farther from the vehicle than the actual distance between the aerial obstacle and the vehicle. FIG. 13A shows the positional relationship between a vehicle 100 and an aerial obstacle 200 at a state in which the aerial obstacle 200 is projected on a road surface. FIG. 13B shows a one-directional bird's-eye view image generated by viewpoint conversion processing that projects an image onto the road surface.
A description of this case is given in an example in which a pole (e.g., a clothes-drying pole) is placed across two stands 201 and 202 exists behind the vehicle 100 as an aerial obstacle 200. As shown in FIG. 13A, the actual distance from the vehicle 100 to the aerial obstacle 200 is assumed to be D1. In this case, when the position of a camera 300 is used as a reference to project an image of the aerial obstacle 200 onto a projection plane that is set at the height of the road surface, the viewpoint of the image of the aerial obstacle 200 is converted into the viewpoint for a position at a distance of D2 (>D1) from the vehicle 100.
As a result, as shown in FIG. 13B, the image of the aerial obstacle 200 is displayed at a position D2 that is farther from the vehicle 100 than the actual distance D1. A dotted line shown in FIG. 13B indicates a guide line that is superimposed on the one-directional bird's-eye view image and is displayed at a predetermined distance (e.g., 50 cm) from the vehicle 100. In the example shown in FIGS. 13A and 13B, the aerial obstacle 200 exists at the same distance (D1=50 cm) as the position where the guide line is displayed. Thus, even though the guide line is displayed for the convenience of the driver, problems exist in that the driver is easily confused/misled since the position where the aerial obstacle 200 is displayed is erroneous.